Concentrations of fenbendazole and of drug metabolites in plasma were
measured in buffalo and cross-bred cattle after single intraruminal ad
ministration at two different doses. Plasma concentrations of the pare
nt compound fenbendazole and the two metabolites, viz. oxfendazole and
fenbendazole sulfone, were much lower in buffalo compared with cattle
, at a dose of 7.5 mg/kg body weight as indicated by lower area under
concentration curve and concentration maximum. At a dose of 15 mg/kg b
ody weight there were corresponding increases in plasma metabolite con
centrations in cattle. However, buffaloes did not show a similar corre
sponding increase.